Cotton cone yarn dyeing,  process mainly consists of the following five steps:

PRETREATMENT

This step primarily removes natural impurities (cottonseed hulls, waxy substances, etc.) and pigmentum from the yarn, enhancing its whiteness and capillary effect to create conditions for dyeing processing.

 

DYEING

Each type of fiber has its unique dyeing characteristics, and yarn dyeing process is formulated based on  properties of cotton fibers (cellulose fibers) and reactive dyes. The process of package yarn dyeing involves applying pressure to dye solution in cone yarn dyeing machine using a pump, allowing the dye solution to penetrate from inner layer to outer layer of package yarn, thereby achieving uniform dyeing.

 

SOAPING

After dyeing, a large amount of hydrolyzed and unreacted dye remains on the surface of the yarn, which must be removed by adding soaping agent and washing under high temperature conditions (known as soaping). The role of soaping is to remove the floating dye on the yarn, improve the color brightness, and meet the fastness requirements of customers.

 

COLOR FIXATION

After soaping, for dark and medium color, fixing agent is added to achieve the processing requirements of subsequent finishing. The function of fixing agent is to form a protective film on the surface of the yarn to prevent dye from falling off during subsequent finishing processes.

 

SOFTENING

During the dyeing process, natural waxy substances on the yarn surface are destroyed, making the yarn feel harder. Therefore, after dyeing, a certain compound is added to the yarn to reduce friction between yarns, facilitating winding and subsequent weaving processes.

 

Bobbin dyeing technology: subjective reasons cause of non-recurrence of yarn through cone yarn dyeing are roughly as below:  winding quality, dye selection, dyeing process, operating factors, management problems, etc.

 

WINDING QUALITY INFLUENCES REPRODUCIBILITY

(1) Bobbin weight: When dyeing by immersion method, the depth of apparent color depends largely on the weight ratio of dye to yarn. In generally, only the number of bobbin is counted when the yarn is put on the cone yarn carrier, no longer weighed again. Therefore, the winding weight determines weight of loading yarn, be weighted after soft winding. Many factory production practices have proved that even without a fixed length meter, it is completely possible to weigh each bobbin and control the weight within the range of ± 1%. Some dyeing plants use "card" to measure the outside diameter, but because of the large error, it is not suitable. The different size of package yarn after dyeing also will get color difference betweent bobbin yarn.

 

(2) Bobbin winding density: The winding density of soft bobbin with direct relationship to resistance of circulation of dyeing liquor . High density, high resistance. Resistance magnitude affects shape of dyeing liquor circulation resistance curve, then affects main circulation pump, affects the circulation flow of the dye fluid, the circulation frequency of dye fluid and number of cycles within specified time are changed, so the amount of dye on yarn is changed, causing the color of yarn to be deep or shallow.

When some bobbin winding density is too small, sometimes the yarn will be out of the "groove", sometimes caused "collapse", the dye liquid will get "short circuit", not only the yarn is washed and dyed unevenly, but also rest bobbin dye liquid circulation will be reduced and cause light color.

 

(3)"Hole exposure" : Because the bobbin and the beam coil are full of holes for the dye to travel through, when the bobbin is not properly wound, or the reciprocating distance is not enough, "hole exposure" will occur. When dyeing, because the warp shaft is placed vertically in the main body of high pressure cone yarn dyeing machine, if winding is too loose, the yarn will fall due to gravity after wetting at sometimes, resulting in upper "hole exposure". The dye liquor will "short circuit" from the "exposed hole", not only wash the yarn on the end of the bobbin, but also affect the flow capacity of other bobbin.

PRETREATMENT INFLUENCES REPRODUCIBILITY

Many dyeing plants don't pay attention to pre-treatment. Actually, many problems in dyeing processing because of ingnoring do enough pre-treatment. Impurity removal degree, whiteness, pH value after washing, purification of hydrogen peroxide after bleaching, amount of alkali carried by mercerized yarn, different tension affect gloss. When dyeing bobbin yarn, pre-treatment, dyeing and post-treatment are carried out in the same high pressure bobbin dyeing machine, and the pre-treatment effect is also different.

Generally, the dyeing factory pays more attention to force determination and weighing of dyes，but less attention is paid to the force determination and weighing of other chemicals. 

Caustic soda, soda ash, hydrogen peroxide is not analyzed, only calculated according to instructions, dye liquor are rarely titrated. So pre-treatment effect is different, causes difference of color depth and hue.

As mentioned, paying attention to compatibility, compatibility, sensitivity and quality of dyestuff, in order to ensure reproducibility.

 

RATIONALITY OF DYEING TECHNOLOGY INFLUENCES REPRODUCIBILITY

Although selecting appropriate dye, the dyeing process is designed not reasonable, there also be cylinder differences.  Such as temperature design, heating rate, holding time, amount of additives and feeding method scientificity, the rationality of post-treatment process design will affect the dyeing amount of dyestuff resulting in color difference.

Such as adding reactive dye solid alkali, fixation and hydrolysis of reactive dyes have a lot to do with the pH value of dye bath, the scientific feeding method is to maintain the Pu value at a fixed value (such as pH value is 11.5), which is related to the feeding method and feeding rate, if one-time feeding or feeding fast and slow all will cause pH fluctuations, amount of fixation and hydrolyzed dyes is different, finally eflects the different shades of light.